2.Refraction of the Human Eye and Methods of Estimating the Refraction by James Thorington (1916)"The left eye is also indicated in one of three ways: L, Lt, or OS, the last from
the Latin for left eye, oculus sinister. . A prescription may call for any ..."

3.Oculo-refractive Cyclopedia and Dictionary by Thomas George Atkinson (1921)"Speaking simply, an absence of squint. OD An abbreviation for the right eye (Oculus
dexter). OS An abbreviation for the left eye (oculus sinister). ..."